The present invention relates, in general, to electronics, and more particularly, to methods of forming semiconductor circuits.
In the past, the semiconductor industry utilized various methods and circuits for forming the error amplifier of a power supply control system. Advances in technology increased the demand for more efficient and more accurate power supply control systems. Often, systems required the ability to change the value of the output voltage of the power supply system under the control of an external control system such as a micro-computer. The external control system typically sent a signal to the power supply control system in order to change the value of the output voltage. FIG. 1 illustrates an error amplifier of a typical prior power supply control system 10. System 10 had a PWM control section 17, a power driver stage 18, an error amplifier 14, and a reference voltage 16. Error amplifier 14 included an operational amplifier 15 in addition to a compensation and gain control network that included a first impedance 12 and a second impedance 13. Impedances 12 and 13 typically included resistors and capacitors that were used to provide high frequency stability for changes in the input voltage (Vin) applied to amplifier 14. One problem with these power supply controllers was accuracy. Often, the error amplifier circuit had tracking errors which caused the output voltage to have inaccurate and unstable changes when the control system requested a change in the value of the output voltage. Such inaccuracy and instability detrimentally affected the operation of the control system that used the output voltage of the power control system.
Accordingly, it is desirable to have a power supply controller that does not have tracking errors, that can accurately change the value of the output voltage, and that maintains stability during the output voltage change.
For simplicity and clarity of illustration, elements in the figures are not necessarily to scale, and the same reference numbers in different figures denote the same elements. Additionally, descriptions and details of well-known steps and elements are omitted for simplicity of the description. As used herein current carrying electrode means an element of a device that carries current through the device such as a source or a drain of an MOS transistor or an emitter or a collector of a bipolar transistor, and a control electrode means an element of the device that controls current through the device such as a gate of an MOS transistor or a base of a bipolar transistor. Although the devices are explained or illustrated herein as certain N-channel or P-Channel devices, a person of ordinary skill in the art will appreciate that complementary devices are also possible in accordance with the present invention.